Hundredth monkey effect

The hundredth monkey effect is a hypothetical phenomenon in which a new behavior or idea is claimed to spread rapidly by unexplained means from one group to all related groups once a critical number of members of one group exhibit the new behavior or acknowledge the new idea.[1]

One of the primary factors in the promulgation of the story is that many authors quote secondary, tertiary or post-tertiary sources which have themselves misrepresented the original observations.[1]

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The account of such a phenomenon originated with Lawrence Blair and Lyall Watson in the mid-to-late 1970s, who claimed that it was the observation of Japanese scientists.[1]

The story of the hundredth monkey effect was published in Lyall Watson's foreword to Lawrence Blair's Rhythms of Vision in 1975,[2] and spread with the appearance of Watson's 1979 book Lifetide. The account is that unidentified scientists were conducting a study of macaque monkeys on the Japanese island of Koshima in 1952.[3] These scientists observed that some of these monkeys learned to wash sweet potatoes, and gradually this new behavior spread through the younger generation of monkeys—in the usual fashion, through observation and repetition. Watson then concluded that the researchers observed that once a critical number of monkeys was reached, i.e., the hundredth monkey, this previously learned behavior instantly spread across the water to monkeys on nearby islands.

This story was further popularised by Ken Keyes, Jr. with the publication of his book The Hundredth Monkey. Keyes's book was about the devastating effects of nuclear war on the planet. Keyes presented the hundredth monkey effect story as an inspirational parable, applying it to human society and the effecting of positive change.[4]

In 1985, Elaine Myers re-examined the original published research in "The Hundredth Monkey Revisited" in the journal In Context. In her review she found that the original research reports by the Japan Monkey Center in Vol. 2, 5, and 6 of the journal Primates are insufficient to support Watson's story. In short, she is suspicious of the existence of a hundredth monkey phenomenon; the published articles describe how the sweet potato washing behavior gradually spread through the monkey troupe and became part of the set of learned behaviors of young monkeys, but Myers does not agree that it serves as evidence for the existence of a critical number at which the idea suddenly spread to other islands.

An analysis of the appropriate literature by Ron Amundson, published by the Skeptics Society, revealed several key points that demystified the supposed effect.

Unsubstantiated claims that there was a sudden and remarkable increase in the proportion of washers in the first population were exaggerations of a much slower, more mundane effect. Rather than all monkeys mysteriously learning the skill it was noted that it was predominantly younger monkeys that learned the skill from the older monkeys through observational learning, which is widespread in the animal kingdom;[8] older monkeys who did not know how to wash tended not to learn. As the older monkeys died and younger monkeys were born the proportion of washers naturally increased. The time span between observations by the Japanese scientists was on the order of years so the increase in the proportion was not observed to be sudden.

Claims that the practice spread suddenly to other isolated populations of monkeys may be called into question given the fact that at least one washing monkey swam to another population and spent about four years there and also the monkeys had the researchers in common. Amundson also notes that the sweet potato was not available to the monkeys prior to human intervention. The number of monkeys in the colony was counted as 59 in 1962 indicating that even in numbers no "hundredth monkey" existed.[1][8]